1. Field of the Invention
The present invention relates to a cell switch module, a transmitter and an active/standby switching method in such a transmitter, and more particularly to switching executed at the time of up-grading a network.
2. Description of the Related Art
In the known public transmission network, audio signals and data information are transmitted to be processed via an infrastructure of SONET (Synchronous Optical Network) in a format of STM (Synchronous Transfer Mode). Such service signals according to the STM format are accessed, in each transmitter, at an STS-1 (Synchronous Transport Signal: 51.84 MHz) level conforming with the SONET frame format or a VT (Virtual Tributary: 1.726 MHz) level. External interfaces employed therefor conform with OC-48 (optical signal: 2.4 GHz), OC-12 (optical signal: 600 MHz), OC-3 (optical signal: 150 MHz), DS3 (electric signal: 44.736 MHz), DS1 (electric signal: 1.544 MHz) and so forth. Further, recently, there is practically used of a data information service which is based on the ATM (Asynchronous Transfer Mode) signal format to realize effective utilization of transmission lines and the band of transmission equipment.
In laying an optical fiber network for use in SONET or the like, the construction thereof by the network service contractor concerned is carried out on the basis of a long-term plan since the construction costs much and the required term for construction of such fiber network is long. On the other hand, it is expected that demands for digital data services using optical fiber networks as transmission lines will increase rapidly after initial diffusion, as represented currently by the Internet. In order to comply with the circumstances thus changing so fast, it is considered necessary to develop an improved transmitter which has a high-speed optical line terminator with a great transmission capacity per optical fiber and a fast digital line terminator adapted for transmitting, via the same transmission channel, both the conventional telephone service where the demand of transmission information is predictable with relative facility and the aforementioned digital data service, and is capable of freely changing, in accordance with needs of such services, the ratio of using such services (e.g., by increaseing the band of ATM cells while correspondingly decreasing the band of data signals other than ATM cells, such as DS1 TDM or DS3 TDM).
Since some modification or extension of such service structure is carried out after practical running, it is necessary to up-grade the same in a manner to render the harmful influence least on the service network being currently used. For example, loss of ATM cells needs to be minimized at the time of any modification or extension. However, none of the known transmitters adapted for handling both STM and ATM signals is equipped with an ATM cell switching function and another function of freely changing the band of ATM cells and that of other signal, although both STM and ATM signals can be transferred via the same optical fiber.
It is therefore an object of the present invention to provide a cell switch module which is capable of switching ATM cells with any other data signal and still is capable of freely changing the band of ATM cells.
Another object of the present invention resides in providing a cell switch module capable of minimizing loss of cells in a cross-connected state of ATM lines to be updated or extended, or in up-grading control software employed therein.
It is a further object of the present invention to provide a transmitter wherein none of ATM cells is sent in duplication when active/standby switching is executed for up-grading.
And a still further object of the present invention is to provide a network adapted to perform, through manipulation under remote control, active/standby switching for up-grading.
In accordance with an aspect of the present invention, there is provided a cell switch module equipped with a unit cell switching function. The module comprises a plurality of input ports for inputting cells thereto respectively; a plurality of output ports for outputting cells therefrom respectively; and cell switching control means placeable in either an active state or a standby state, wherein a decision is made as to whether each cell inputted to the relevant input port is a specific first cell or not, and a control action is so executed that, if the result of the decision signifies that the cell is said first one in the active state, any subsequent cell inputted thereafter to the input port is not switched, and if the above result signifies that the cell is said first one in the standby state, any subsequent cell inputted thereafter is switched. Preferably, the cell switch module further comprises a queue empty detection means for detecting whether the all cells switched by the active cell switch module in response to an active/standby switching instruction have been completely outputted from the output ports.
In the structure mentioned, the cell switching operation is brought to a stop in the active cell switch module in response to a detection of the first cell as a trigger by the cell input control means, and the cell switching operation is performed in the standby cell switch module. Any subsequent cell inputted after the first cell to the relevant same line is switched in the standby module but not in the active module. Thus, due to such a double structure where both active and standby cell switch modules are prepared, the cell switching operation is not performed in duplication with regard to any of subsequent cells inputted after the first cell to the relevant same line.
In accordance with another aspect of the present invention, there is provided a transmitter which comprises a first cell switch module as the above active one and a second cell switch module as the above standby one; a plurality of selectors for selecting, in response to a select signal, signals obtained from two output ports corresponding respectively to the first and second cell switch modules; and a switching control means for generating the select signal to instruct switching from the acting module to the standby one on the basis of the result of the detection obtained from the queue empty detection means. When the active queue empty detection means has detected that the all cells are outputted from the all output ports of the active cell switch module, the switching control means generates a select signal to instruct switching from the active module to the standby one, whereby the active cell switch module is switched to the standby cell switch module after none of the switched cells is left in the active module, hence minimizing the loss of the switched cells stored in the active cell switch module.
In accordance with a further aspect of the present invention, there is provided a network comprising a plurality of the aforementioned transmitters connected mutually via a synchronous network; and a file server connected to at least one transmitter via a communication line. In the network of the present invention, routing information required with up-grading is sent from the file server to the transmitter via a communication line. The transmitter receives the routing information and then stores the same in a data base file or the like. Meanwhile, the routing information once transferred to the transmitter connected to the file server is sent to the overhead of a synchronous frame prescribed in the synchronous network from the transmitter, and then is further sent to any transmitter which is not connected to the file server. Consequently, the routing information can be down-loaded to each transmitter from the file server in a remote site far from any transmitter, and there exists no necessity of connecting the all file servers to the transmitters, hence curtailing the communication cost. Preferably, switching time information is transferred from the file server to each transmitter, so that each transmitter can perform an active/standby switching operation in accordance with the switching time information, whereby every active/standby switching operation can be performed synchronously in the entire network.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.